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mtDNAsequence analysis[2] indicates a close relationship between the yellow-billed magpie and the black-billed magpie, rather than between the outwardly very similar black-billed and European magpies (P. pica); the two American forms could be considered as one species.

The Koreansubspecies of the European magpie (P. p. sericea) is more distantly related to all other (including North American) forms judging from the molecular evidence, and thus, either the North American forms are maintained as specifically distinct and the Korean (and possibly related) subspecies are also elevated to species status, or all magpies are considered to be subspecies of a single species, Pica pica.

The yellow-billed magpie is gregarious and roosts communally.[5] There may be a cluster of communal roosts in one general area made up of a central roost containing many birds and several outlying roosts with fewer.[5]

Yellow-billed magpie flocks are known to engage in funeral-like behavior for their dead.[6]

The yellow-billed magpie prefers groves of tall trees along rivers and near open areas, though in some cities they have begun to nest in vacant lots and other weedy places. A pair of birds builds a dome-shaped nest with sticks and mud on a high branch.[7] Nests may be 14 meters above the ground and are sometimes built far out on long branches to prevent predators from reaching them.[4] They nest in small colonies, or occasionally alone.[7] Even when nesting close to other birds they may exhibit some territorial behavior.[4] These birds are permanent residents and do not usually wander far outside of their breeding range.[4]

Extra-pair copulation is not uncommon among yellow-billed magpies. After mating, a male will exhibit mate-guarding, preventing the female from mating with other males until she lays the first egg.[8] The clutch contains 5 to 7 eggs which are incubated by the female for 16 to 18 days.[4] Both parents feed the nestlings a diet of mostly insects until fledging occurs in 30 days.[4]

This bird is extremely susceptible to West Nile virus. Between 2004 and 2006 it is estimated that 50% of all yellow-billed magpies died of the virus.[9] Because the bird tends to roost near water bodies such as rivers, it is often exposed to mosquitoes.[5]

The IUCN classifies the bird as a near threatened species.[1] The Nature Conservancy places it in the vulnerable category.[10] Besides West Nile Virus, threats include loss of habitat and rodent poison.[4] The bird has a limited area of distribution but is widespread throughout the area and still common in many places.[4]